Back to the Beginning
by POTOPhan09
Summary: In a world where Chara takes over Frisk's body after the first Genocide run, and Frisk has no control what so ever. But Frisk is able to Reset and take back control of her body for the next run. But what if Sans is finally sick of it all and grabs Frisk when she's still unconscious from the first fall into the Underground? Sans X Frisk. Rated M for later chapters.
1. Prologue

A/N: Hey! I'm back! Sure, I'm back with something completely different! But I'm back. God, I didn't even know where this came from but... Oh well. Just wanted to finish at least the Prologue before I fell asleep, so here it is! This is a Sans X Frisk and it will probably get smutty in future chapters, so fair warning for that. I'm using Frisk's POV for the prologue because it was originally written for Sans X Reader, but I changed my mind at the last second. Anyway, I do not own any of the Undertale characters. So please read, review, and I hope you enjoy!

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Prologue

(Frisk POV)

Chara smiles evilly as she looks over the city she decimated. She was so proud of herself, of the multiple timelines she had done Genocide on, just for the fun of it. All she wanted was to cause pain and destruction, for no true reason. Your consciousness was not in control, and hadn't been since the ending of the first Genocide run. It had been your overwhelming curiosity that had gotten the best of you, you told yourself. You just wanted to see what the differences were from the many Pacifist runs you had already done. Why did you keep resetting just to do the same run? You lose yourself in memories of yourself and your friends, meeting them over and over again. It filled you with happiness just to think of them, but looking out of your own eyes at the world you had helped create, it killed that happiness as easily as it had appeared.

It had started out small, as everything does, but soon, it was like something had been pushing you, knife in hand, to kill your friends, the ones you so dearly loved. And the first time in the Genocide run, in the Judgement Hall… The complete and utter look of betrayal on San's face… You knew then he knew about the resets. Every. Last. One. You curl back into yourself, not wanting to think about that look anymore, knowing it had all been your fault for that run, and for the runs that followed it.

You gave Chara your soul to get the Underground and the World back. That's what you kept telling yourself. You just needed to get through one more run, and Chara would get tired of it all and go away, leaving you alone to pick up the pieces of the Underground during a new reset, but she never did.

Chara never grew tired of the games. Of the blood, the deceit. She enjoyed killing all of your friends, knowing it was your body, your face that they saw when they turned to dust. And every single time, in EVERY Timeline, Sans looked all the more tired, and as much as he called your name, not wanting to fight anymore, he was even starting to lose hope. That's the only thing that kept you here, kept you from going under completely.

You raise your eyes as Chara appears next to you in the space you now occupy in your mind.

"How are you doing, ' _Partner_ '!" Chara said with a sickening grin, her eyes as red as the blood on her knife. You shift your eyes away. You knew that Chara liked to talk and you weren't going to give her that satisfaction anymore. You were done with her games. You didn't want to deal with any of it anymore. You just wanted to live in peace, away from Her. Chara smile grew wider, knowing exactly what you were thinking.

"Awwww, ' _Partner_ ', that's not very nice to think! We're in this together! I could never have done this alone! And we'll be together for as long as you keep holding on, which if I feel like keeping you around, could be forever!" You cringe at that thought, not wanting to even think about it that way. Bright yellow light bathed the two of you as the Reset and Continue buttons appeared before you. Chara smirked then, and side glanced at you.

"Well, I hope you're ready for another round! This is really getting fun now!" Your eyes shot open in fear as you instinctively jump at her as she is reaching for the reset button, knocking her to the side because of her surprise. You stumble, and your hand accidentally lands on the Reset button. All you hear before you black out was a scream of rage.


	2. Chapter 1

A/N: Hey! Back again! I know that was fast (not really) for posting the next chapter, but I guess I just wanted to write? I'm literally using Google Docs, and it sucks when you get to the second page, so I have to keep making the font smaller if I want to make the chapter longer. I just wanted to get the basis for the story out. This chapter brings a little surprise, and no, I'm probably not going to have it explained for several chapters. Hehe I'm mean! Anyway, I might do a chapter a week after this or so. Depends on my inspiration.

So I don't own Undertale or any of it's characters. I wish I did though!

Please Read, Review, and Enjoy!

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Chapter 1

Shooting up from his bed in a cold sweat, Sans gasps, almost as if he's desperate for air. He breathes heavily for a few seconds, trying to take everything in around him while gaining his bearings. He looked around his room in Snowdin, seeing nothing different from the last time he was here before he went to…

"Damn that kid…" Shaking his head, he put his face into his hands, the feeling of dread still crawling up his spine. He was sick of the Resets, of living this nightmare over and over again, and being the ONLY one to remember them. He just wanted it to stop, to be done with. Was it so bad for him to want to hope that one of these times it would all stop? Probably. But enough was enough.

He looked up, his left eye glowing a fiery blue, his other eye socket completely empty. He instantly teleported (Still only in shorts and white t-shirt) to the bed of yellow flowers in the Ruins. All the Resets started over from the same point - when Frisk fell into the Underground in the first place. As Sans glared down angrily at the kid, he immediately noticed something was off. Different.

Frisk laid on the bed of flowers on her side, but he couldn't see her face. Long tendrils of brown hair hung over her face and down her body, which had a lot more skin showing (Imagine an 18-year-old wearing 7-year-old clothing and go with that). He shook his head and grabbed the human by the wrist, pulling her up and over his shoulder. He would look into it more later. For now - before Flowey showed up - he would lock her away so she couldn't cause anymore damage to this reset Underground. He and Frisk disappeared in a flash of light.

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Consciousness did not come easily to Frisk. It was like being underwater, and trying to kick to the surface, fighting against the current along the way. She didn't feel Chara's influence anymore, but she would look into that later. She had never known how hard it could be, fighting to open your own eyes as it was now. She was so close to breaking through the surface, she could feel it. She wanted out of this suffocating darkness. It reminded her too much of Chara.

Frisk gasps as she finally breaks the surface, only to start coughing as she wakes up. She didn't know where she was, but the floor she was laying on was cold. Nothing like the flowers she was use to waking up in after a Reset. This was different. She hadn't even opened her eyes yet, but she started to shivering as it was cold wherever she was. Was she already in Snowdin? Who had brought her here? So many questions formed in her mind.

That was when she noticed the bottom of her shirt was rubbing against her mid-drift, her shorts were ripped and unbuttoned, and both felt way too tight now. She rolled onto her back, hands above her head, because for some reason she couldn't move them apart. She also felt something cold and hard brushing against her wrists and keeping them together. She finally was able to open her eyes and look up at her wrists. They were held together by… Bones?!

She looked down at herself, still shocked by that, not noticing she was now looking through long hair that was hanging in her face. She… She had boobs!? Her body had greatly changed from the last Timeline. Now, she had the body of an 18-year-old girl. She now had a full bust, a small waist, and rounded hips. Her legs and arms were both longer than before as well. She inwardly screamed from all the changes, and outwardly, she just stared down at herself, still not believing that this was her body. She was suddenly brought out of her shock by the opening of a door, and momentarily blinding her by the light that was coming in from outside. She whimpered as the light was actually bright to her, her eyes not use to any light while Chara had been in control.

"Hehe… I see you're awake now, Kid…" Sans stepped into the shed and shut the door, turning the lights on and getting his first good look at Frisk since he had brought her here. Instantly, a blue like flush spread over his cheekbones. Even after noticing the differences in the Ruins, this was not what he was expecting. Laying on her back, hands bound above her head with her hair fanned out around her, and in what were now skin tight clothes… He shook his head again, still not noticing Frisk was shivering so much from the cold.

"S-Sans… W-what…." Frisk whimpered again. Even her voice was deeper. This entire situation was frightening to her. And she was just so cold…

He must have finally noticed she was shivering so bad that he looked at her face.

"So, Kid, how does it feel now to be on the receiving end of the stick?"

"S-Sans, p-please… I… I didn't m-mean to…" Frisk tried to reason with him, but her voice was already failing her. She was just… so cold… and so tired… She closed her eyes again as Sans eye sockets grew wider and his white pupils disappeared.

"No, Kid, Don't -" Was the last thing Frisk heard before darkness took her in again.


	3. Chapter 2

A/N: Hey! Another Chapter! So I don't honestly know where I'm going with how Sans is in this, so the chapter is still shorter than I would like. So far, this is literally a slow going story, and I am sorry for that. I like going into detail with a lot of things.

I don't own Undertale or it's characters :P

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Chapter 2

The darkness was different from when she had been under Chara's control. It was softer, more welcoming. Frisk wanted to stay in it forever. No pain, no agony, no memories of what she had done. She stayed like that for several hours, and when the light started to invade the warm dark, Frisk fought to stay unconscious. She wanted to stay in the dark. The light, however, was bright, unyielding, and harsh. She screamed as the light took over her blessed dark. And her eyes shot open, dark brown eyes instantly closing again from the sudden brightness of the room.

She whimpered. Apparently, her eyes still weren't use to the brightness of the outside world and it still hurt to open her eyes. She shifted, feeling a mattress underneath her as well as a large sweatshirt on her and a comforter covering her body, keeping her warm. She wasn't in the shed anymore, which was a relief. She wondered where she was. She cracked open an eye, trying to take in her surroundings without causing her eyes anymore pain.

As she looked around the room, confusion clouded her thoughts. Where was she? She had never seen this room while she was in Snowdin through the countless runs she had made. There, for some reason, was a treadmill in the middle of the room, and a sock pile in right corner by the door. She looked to the opposite corner in front of the bed and saw a… Was that a tornado of trash and books? Both eyes open now, she turned onto her back, and tried to sit up, but her hands were still being held together by bones now in front of her. She groaned and shifted herself until she was able to prop herself with her back against the wall underneath the window so she could sit up. She could already see bruises forming underneath the bones on her wrist and she winced when she even slightly moved them. Looking down at herself again, she looked at herself with disbelief. She was wearing San's sweatshirt. He must have put it on her at some point when she was unconscious, but just with the fact that she had it on… It was only zipped up part of the way, so she could see that she… wasn't wearing any clothes underneath.

She shook her head again and her attention returned to the mini tornado across the room from her. It was… Interesting to say the least. As she was looking around the room some more, the door opened and closed quickly, Sans having come into the room to check on her. As she looked over at him, she tensed and plastered herself against the wall, wanting to be anywhere but here right now. He looked at her with such a hatred… She shivered as she felt her sins crawling up her spine.

"So, you're awake again, kid…" Sans looked at her, huddled against the wall in fear. Her eyes, for once, were open and not blood red. Tears were filling her eyes just ready to spill over. She was so scared, she was shaking, and not from the cold this time. He didn't really understand it, what with how she had killed all the monsters over and over and over again.

"S-Sans….?" Frisk whispered in a small voice and she looked back down at her bone-bounded wrists. She chuckled awkwardly and looked back up at him. "So, got a _bone_ to pick with me? He - he…" Her bad pun just made Sans more confused. She was trying to make this situation funny? She softly giggled as memories of his past puns.

"A-anyway… Now that we got that out of the way… Can you please take the b-bones away from my wrists?" She shifted her wrists and winced, the pain lacing up both of her arms. A whimper escaped her both as she started to curl into herself

Sans look at her in disbelief. For all the stuff she had done in the past Timelines… She thought he would just trust her like that again? Be like how they were in the first run, when she really first had fallen? That was impossible. He looked down at her, and for the first time, noticed that the zipper on his sweatshirt covering the kid was only half-way zipped up, and with the different body, a toned stomach and lots of cleavage showed between the zippers of the sweatshirt. Her hair was also flowing down her back and pooling around her waist.

Frisk tilted her head to the side as a blue flush covered Sans cheekbones. She followed his line of sight and blushed herself. Of course, from her point of view, she could see a lot more than he could. She pushed her arms together and pulled her hands up to rest under her chin so nothing was showing.

"Um… S-so could you say something…? A-and stop looking at me like that…" Frisk looked to the side, still blushing.

Sans shook his head and looked at her, still confused at why she looked so different. He had made up his mind and he took a deep breath to calm himself down before he started speaking.

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Aaaaaand Cliffhanger! Man I'm a butt. Like I said, slow going. I just had the sudden inspiration for the Prologue and then bits and pieces here and there, but putting them together is the hard part. I'm gonna try my best though!


	4. Chapter 3

Heyyyyyy! I'm Baaaack! Had a really bad case of writers block, and I just got back into Undertale, as well as finally got back to playing the game. I finally got past Miss Muffet! But now I'm stuck on Mettaton... Anyway. I also changed Chara to a He, because I think it's more interesting that way! :)

I don't own any of the characters or Undertale. (I wish!)

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Chapter 3

Before Sans could even get a word in, the front door of the house slams, and a loud yell reverberates through the house. Sans curses under his breath, taking one more look at Frisk and stalks out of his room, only really leaving when he's locked the door behind him. Frisk looks on in shock, as tears start to pool in her eyes. She knows that voice all too well. That kind face that only wants to solve puzzles, be the best, and have friends. A small whimper leaves her lips as she buries her face in her still bound hands. She doesn't want to face any of them. Now that she's free, she just wants to get out of the Underground, and hopefully never lays eyes on another 'Reset' button again.

 _ **"But, 'Partner'..."**_

Frisk jumps and almost screams. Tears start falling down her face, but now not only in sorrow, but in fear...

"N-no... It can't be... I beat you..." Frisk whimpers and fights to get free, even though she knows Chara is in her head.

 _ **"We're in this together, remember? I can't do this without you..."**_ She can almost feel Chara's fingers, like a caress, trailing down her spine. Frisk shivers, the tears keep falling. She doesn't want to go back to the dark, and she doesn't want to keep killing her friends. And this is how it started in the first place; Chara whispering sweet nothings in her ear on how different each reset could be, if you just took one life. He then guided Frisk's hand, showing her what could be possible if she just carried through with the knife in hand. And it was different, because Frisk was no longer the one in control. She shakes her head, digging her nails into the palms of her hands so hard that blood started to bead around her nails. Sans face popped into her head from the first Genocide run. The pure betrayal on his face had made her want to sink deeper into herself at first. Now, it's making her stronger so it won't happen again.

"N-no, Chara... You're not... in charge... Go back... To whatever Hell you crawled out of..." Frisk almost growls at herself. She is DETERMINED to make sure that Chara does not get control again. She can almost imagine Chara cocking his head to the side, with that sick grin on his face.

 _ **"We'll see... I'll leave you alone for the time being... Don't worry, you'll see that the Monsters you remember aren't the same... You'll see..."**_

Frisk sighed in relief as Chara's presence reseeded, but she knew she was still there. Tears still fell down her face as the sorrow came back full force. Papyrus... was in the house...

The door unlocked and opened just enough for Sans to get in. Of course, that's when she noticed, from her struggling, the sleeves of the hoody had been pushed up, and blood was now running down her wrists and from her palms. She looked up at Sans, whose eyes were closed, almost in frustration if he had more of a facial expression... Wait... Frisk giggled to herself as she looked over at Sans.

"Hey, Sans, why the long face?" She bit her lower lip to keep from busting out laughing from her little pun. That's when he looked up at her again, in complete confusion.

"Did you just..." That's when he finally notices the blood running down her arms and hands. She looks down, her wrists and hands now numb from the abuse, and a little light headed from the blood loss. Frisk still looks up at Sans, eyes closed and she smiles.

"Looks like... I made a mess... I'm... Sorry..." She starts to get dizzy, starting to pass out again. Her last thought is that she really wishes she would actually stop passing out. It was getting old. Then... Darkness again.

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As the Kid falls back, passing out from blood loss, Sans lunges to catch her before the back of her head hits the wall. Even in unconsciousness, tears continue to fall from Frisks eyes. He just looks down at her in confusion, like he's seeing her for the first time again. It had been - he didn't even know a number at this point - resets since he had heard her crack a pun like that.

A small smile appears on his face as he thinks of the times before the Genocide runs. Sure, the constant repeats sucked, but Frisk, during one of the earlier reset, explained to him that she enjoyed meeting her friends over and over again and recreating the bond that they all had. She had never had that at the Orphanage, and she was positive she would never find that anywhere else. Of course, she said this with no idea that Sans kept his memories through every reset. And with that thought, Frisk moved slightly, whimpering.

"Sans... No... N-no more... Please... I don't... want to..." Sans cheek bones instantly went blue as his mind went straight into the gutter. As Frisk gripped her chest as if in pain, the blush instantly went away. She must be dreaming of the resets where he killed her over and over again... Instantly, Sans good mood disappeared and he was pissed all over again. He waved his hand over her wrists and the bones disappeared. He needed them gone to bandage her wrists, at least. Wouldn't do any good if she bled out and reset again. This reset was different, since Sans interfered and brought Frisk here to begin with.

As he finished bandaging up her wrist, she started, shifting against his hip bone. Sans tensed, lightly taking her wrists in his and binding them together with magic. This would speed her healing, and keep her bound without her hurting herself again. He gets up and heads towards the door. Paps had stopped by to see why he wasn't at his sentry post, and why he hadn't re-calibrated his traps in 8 days. Just like before, but a difference destination. He takes his short cut straight to his post, leaving the kid - the anomaly - on his bed.

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Hope you like it! Read and Review Please!


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